Internal combustion engines are fueled by an air-fuel mixture combusted in cylinders. Control of the air-fuel mixture ratio is important in optimizing the performance of an internal combustion engine and resultant exhaust gas emissions.
Prior injector controls are designed to provide precise control of the air-fuel mixture in steady state operations. The optimum air-fuel mixture ratio is normally about 14.6:1. Under transient conditions; e.g., during acceleration or deceleration, the air-fuel ratio can change from the optimum ratio, which is referred to as running lean or rich, for a time on the order of one second or more. Factors such as engine temperature, manifold pressures, fuel vapor pressure and engine air mass flow rates affect the degree to which air-fuel ratios deviate from ideal conditions.
Fuel injectors generally direct fuel sprayed by a nozzle onto a wall of an intake port or valve surface. Fuel supplied as a spray on the wall of an intake port either vaporizes or coats the wall of the intake port as a liquid or film which wets the wall. A portion of the fuel wetting the walls of the intake port and valve creates a liquid film which flows on the walls. Liquid fuel film flows at a slower speed than the inducted air and fuel vapor. Some of the liquid fuel film evaporates as it flows in the walls.
Under ideal circumstances, all of the fuel supplied is in the form of a vapor. However, on initial start up or during rapid acceleration, relatively cool temperatures of intake port wall or rapid increase in fuel supplied prior to increasing engine speed results in the formation of a sizeable deposit of liquid fuel film on the intake port wall.
Applicant's technical paper entitled "Spray/Wall Interactions Simulation", Servati, Hamid B. and Herman, Edward W., SOCIETY OF AUTOMOTIVE ENGINEERS, Paper No. 890566, explains injector spray wall interactions for the purpose of optimizing injector location, design and spray patterns for improving engine performance. As explained in that paper, two phenomena are considered in fuel vaporization: (i) conductive fuel vaporization; and (ii) convective fuel vaporization. Conductive vaporization is a function of fuel volatility wherein fuel contacting warm surfaces results in lower boiling point hydrocarbons evaporating while the high end hydrocarbons with low vapor pressure remain on the walls in liquid form. Convective vaporization results from turbulent forced convection of fuel into the air stream. Fuel properties, such as viscosity, density, diffusivity, fuel temperature and wall surface temperature, air flow, intake manifold pressure, charge temperature, engine speed and the area of the vaporization surface all affect convective fuel vaporization.
Fuel is transported into the engine cylinder in gaseous and liquid form, the liquid form being provided by the flow of a fuel film on the wall to the intake port.
While these engine operation conditions have been known, utilization of this information as a basis for an injector control system has not heretofore been developed.